Gasoline hydrodesulfurization

ABSTRACT

Selective hydrodesulfurization of an olefinic gasoline fraction, e.g., cracked gasoline, is accomplished by use of a catalyst of a noble metal supported on an acidic support. Such a catalyst reduces the sulfur content to acceptable levels, while minimizing hydrogenation of olefins to retain octane quality of the treated gasoline fraction.

1. FIELD OF THE INVENTION

[0001] The present invention relates to upgrading hydrocarbon streams containing organo-sulfur compounds. It more particularly refers to a process for desulfurizing olefinic naphtha boiling range hydrocarbon fractions containing organic sulfur impurities.

2. BACKGROUND OF THE INVENTION

[0002] Two major portions of a gasoline fraction may be produced by fluidized catalytic cracking (FCC) or thermal cracking of a heavy petroleum fraction. The cracked gasoline forms a major part of the gasoline product pool in the United States and they are the major source of sulfur in the gasoline pool. As a result of more stringent environmental regulations, it is required that the sulfur content of gasoline is further reduced. In this respect, in processing a cracked gasoline fraction, it is required to further reduce the sulfur content thereof and, in many cases, it may be required to reduce sulfur content of a gasoline fraction by 90-99%. This increased reduction if necessitated by regulations that may require refiners to target sulfur content in the final blended gasoline in the order of 30 parts per million.

[0003] Hydrocarbons of any of the sulfur containing olefinic fractions, which boil in the gasoline boiling range, causes a reduction on the olefin content and consequently a reduction in the octane number. As the degree of desulfurization increases, the octane number of the treated product decreases.

3. SUMMARY OF THE INVENTION

[0004] It has now been discovered that the problems encountered in the prior art can be overcome by the present invention, which provides a process for reducing sulfur content of olefinic hydrocarbon stream while substantially maintaining the olefinic content, more particularly octane number. The process includes contacting an olefinic hydrocarbon stream containing organic sulfur with a noble metal catalyst supported on a solid acid support. The containing organic sulfur with a noble metal catalyst supported on a solid acid support. The metal catalyst is a VIII noble metal(s) which may be used with or without a metal(s) catalyst that is not a noble metal combined with other metals from Group VI.

[0005] From the literature it is known that bimetallic noble metal catalysts have excellent activity for aromatic saturation (U.S. Pat. No. 5,345,612; U.S. Pat. No. 5,308,814; U.S. Pat. No. 5,271,828; U.S. Pat. No. 5,225,383; U.S. Pat. No. 5,151,172; U.S. Pat. No. 5,147,626). From this work it would be expected that such catalysts would also be good catalysts for olefin saturation. Surprisingly, we have found that noble metal catalysts supported on acid supports are highly effective in desulfurization of olefinic hydrocarbon streams while substantially maintaining olefin content.

4. DETAILED DESCRIPTION OF THE INVENTION

[0006] In order to further reduce the sulfur content, it is desirable to effect such a reduction without decreasing the olefin and aromatic content of the gasoline stream in that such a reduction results in a loss of octane number.

[0007] The present invention is directed to providing for improved hydrodesulfurization wherein the sulfur content of a gasoline fraction can be reduced to required levels, without high olefin and aromatic hydrogenation, which leads to high octane losses.

[0008] More particularly, in accordance with an aspect of the present invention, a gasoline fraction is subjected to hydrodesulfurization conditions in the presence of a catalyst that contains at least one noble metal from Group VIII supported on a solid acid support and which may also contain one or more other metals, e.g., a Group VIB metal (Mo, W, Cr), or Group VIIB metal (Re, Mn, Tc). The noble metal is preferably at least one of platinum, palladium, and ruthenium, with platinum and/or palladium being particularly preferred. In a preferred embodiment, the catalyst includes both platinum and palladium. The noble metal is generally present in the catalyst in a sulfided form. The term “metal” or “noble metal” includes the sulfided form of a metal.

[0009] Temperature programmed desorption (TPD) of basic molecules such as ammonia, isopropylamine (IPA), pyridine, n-butylamine, etc. is frequently used to characterize the acid strength as well as acid amounts on a solid surface (G. Wang, H. Itoh, H. Hattori, K. Tanabe, J. Chem. Soc., Faraday Trans. 1, 79, 1373 (1983)).

[0010] In accordance with the invention, the solid acid supports are those supports that, when tested by the hereinabove-described temperature programmed desorption of ammonia or isopropylamine (IPA), desorbs at least 100 micromoles of ammonia or IPA per gram of support material at temperatures above 100° C. Preferred materials are those that desorb at least 25 micromoles of ammonia per gram of support at temperatures above 200° C. and still more preferred are those that desorb at least 20 micromoles of ammonia per gram of support at temperatures above 300° C.

[0011] Although as hereinabove described, the support is an acidic support, the selected acid support should not have such a high level of acid sites that the catalyst in effect becomes a cracking catalyst in that cracking of the feed lowers the octane number.

[0012] In accordance with the above definition, a summarized list of acidic supports is given in Table 1. TABLE 1 IMPORTANT SOLID ACIDS ACID TYPE EXAMPLES 1. Natural Clay Kaolinite, bentonite, attapulgite, Minerals montmorillonite, clarite, fuller's earth, zeolites (X, Y, A, H-ZSM etc), cation exchanged zeolites and clays 2. Mounted Acids H₂SO₄, H₃PO₄, CH₂(COOH)₂ mounted on silica, quartz sand, alumina or diatomaceous earth 3. Cation Nafion, Amberlyst 15, Amberlite IR-120, Exchange Nafion-silica composite Resins 4. Charcoal heat- treated at 300° C. 5. Metal Oxides ZnO, CdO, Al₂O₃, CeO₂, ThO₂, ZrO₂, SnO₂, and Sulfides PbO, MnO₂, As₂O₃, Bi₂O₃, Cr₂O₃, Sb₂O₅, Nb₂O₅, Ta₂O₅, V₂O₅, MoO₃, WO₃, CdS, ZnS 6. Metal Salts MSO₄ (M = Mg, Ca, Sr, Ba, Cu, Zn, Cd, Fe, Co, Ni), M(NO₃) ₂ (M = Zn, Ca, Bi, Fe, Ca), M₂ (SO₄)₃ (M = Al, Fe, Cr), KHSO₄, (NH₄) ₂SO₄, Fe(NO₃)₃, MPO₄ (M = B, AL, Cr, Fe), Cu₃ (PO₄) ₂ (M = Cu, Zn, Mg, Ni), Cu₃(PO₄)₄ (M = Ti, Zr), AgCl, CuCl, CaCl₂, AlCl₃, TiCl₃, SnCl₂, CaF₂, BaF₂, AgClO₄, Mg(ClO₄)₂. 7. Mixed Oxides SiO₂-M₂O₃(M = Al, Ga, Y, La), SiO₂-MO₂ (M = Ti, Sn, Zr, Th), SiO₂-MO (M = Ca, Mg, Be, Sr, Zn), SiO₂-MO₃ (M = Mo, W), Al₂O₃-MO (M = Mg, Zn, Ca, Ni), Al₂O₃-M₂O₃(M = Cr, Mn, Fe), Al₂O₃—Co₃O₄, Al₂O₃—V₂O₅, TiO₂-MO (M = Cu, Mg, Zn, Cd, Ni), ), TiO₂-MO₂ (M = Zr, Sn), TiO₂—V₂O₅ (M = V, Sb), TiO₂-MO₃ (M = Mo, W), TiO₂-M₂O₃(M = Mn, Fe, Cr), ZrO₂—CdO, ZnO—MgO, ZnO—Fe₂O₃, MoO₃— CoO-Al₂O₃, MoO₃—NiO—Al₂O₃, TiO₂—SiO₂— MgO, MoO₃—Al₂O₃—MgO, heteropoly acids 8. Supported Oxides supported on supports like alumina, Oxides silica, titania, zirconia, minerals, clays, zeolites, molecular sieves, and mixed oxides 9. Synthetic Microporous and mesoporous aluminislicates, zeolites or AlPO₄'s, SAPO's, MePO₄'s molecular sieves

[0013] A solid superacid is defined as a solid whose acid strength is higher than the acid strength of 100% sulfuric acid” (K. Tanabe, M. Misono, Y. Ono, and H. Hattori, NEW SOLID ACIDS AND BASES-THEIR CATALYTIC PROPERTIES, p.3, Elsevier, Amsterdam, 1989) . Since the acid strength of 100% sulfuric acid expressed by the Hammett (L. P. Hammett, A. J. Deyrup, J. Amer. Chem. Soc., 54, 2721 (1932)) acidity function, Ho, is −11.9, a solid of Ho <−11.9 is called a solid superacid. The kinds of solid superacids are given in Table 2. TABLE 2 Solid Superacids Acid Support SbF₅ SiO₂—Al₂O₃, SiO₂—TiO₂, SiO₂—ZrO₂, TiO₂— ZrO₂, Al₂O₃—B₂O₃, SiO₂, , SiO₂—WO₃, , HF—Al₂O₃ SbF₅, TaF₅ Al₂O₃, MoO₃, ThO₂, Cr₂O₃, Al₂O₃—WB SbF₃, BF₃ Graphite, Pt-graphite BF₃, AlCl₃, AlBr₃ Ion exchange resin, sulfate, chloride SbF₅—HF, SbF₅— Metal (Pt, Al), alloy (Pt—Au, Ni—Mo, Al—Mg), FSO₃H polyethylene, SbF₃, porous substance (SiO₂— Al₂O₃, kaolin, active carbon, graphite) SbF₅—CF₃SO₃H F—Al₂O₃, AlPO₄, charcoal Nafion (polymeric perfluororesin sulfuric acid) TiO₂—SO₄ ²⁻, ZrO₂— SO₄ ²⁻, Al₂O₃—SO₄ ²⁻ H-ZSM-5 zeolite

[0014] As representative examples of suitable acidic supports, there may be mentioned silica-alumina, and particularly, amorphous silica-alumina, an acidic zeolite, such as ZSM-5, USY, beta, ZSM-4, ZSM-5, zeolite Omega, ZSM-11, ZSM-20, ZSM-22, Theta-1, MCM-41, ZSM-35, ferrierite, ZSM-48, ZSM-50, ZSM-57, MCM-22, MCM-36, MCM-48, MCM-56, SSZ-32, and SAPO's, AlPO₄'s, or other MeAPO₄'s.

[0015] As hereinabove noted, in a preferred embodiment, more than one noble metal is employed, with a combination of palladium and platinum giving particularly good result.

[0016] Preferred acidic supports are those that have a pore size wherein the pore diameters are within a range from 0.4 nm to 150 nm. In a preferred embodiment, the surface area of the support is within a range of from 1 m²/g to 1500 m²/g. The catalyst is preferably in particulate form wherein the particles fall within the range of from 0.2 micron to 10 mm.

[0017] In preparing the noble metal catalyst supported on an acidic support, in general, the support contains from about 0.01% to about 5.0% of noble metal, based on noble metal and support, all by weight.

[0018] The present invention is particularly applicable to the hydrodesulfurization of gasoline fractions that have a high sulfur content, and in particular, with a feed sulfur content of at least 100 ppm, and generally at least 500 ppm.

[0019] In proceeding in accordance with the present invention, it is possible to reduce the sulfur content by at least 25%, and preferably at least 90%, by weight, without significantly reducing the olefin and aromatic content. In particular, in a preferred embodiment, the product from the hydrodesulfurization contains at least 30%, and preferably at least 50% of the olefins contained in the feed.

[0020] The hydrodesulfurization may be effected at conditions generally known in the art. In particular, in general, such hydrodesulfurization is effected at a temperature from 200° F. to about 800° F. (preferably from about 300° F. to about 550° F.); a total pressure of from about 50 to about 900 psig (preferably from about 100 to about 500 psig); at a hydrogen feed rate of from about 100 SCF/Bbl to about 5000 SFC/Bbl, and preferably from about 300 to about 3000 SCF/Bbl.

[0021] The hydrodesulfurization may be effected in any one of a wide variety of reactor systems, such as a catalytic distillation column (CD Technology^(R)), a fixed bed, ebullated bed, a fluidized bed, a moving bed, slurry reactor and the like. In the case of a fixed bed, the reactor may contain more than one bed. The catalyst may be in the form of extrudates, pellets, spheres, granules, etc.

[0022] The reaction may be effected in either the liquid or the vapor phase, and is preferably effected in the gas phase for better selectivity.

[0023] The gasoline fraction which is hydrodesulfurized in accordance with the present invention is preferably one in which the 5% boiling point is at least 150° F., and wherein the 95% boiling point is no greater than 500° F., preferably no greater than 400° F. and more preferably no greater than 300° F. As hereinabove indicated, such gasoline fractions are generally produced by a fluidic catalytic cracking or thermal cracking, or may be a coker or visbreaker naphtha.

[0024] In accordance with the present invention, it is possible to significantly reduce the sulfur content of such gasoline fractions, while maintaining a high selectivity with respect to hydrodesulfurization, whereby hydrogenation of olefins and aromatics is reduced, whereby the product retains a high proportion of the octane number of the feed. For example, in a preferred embodiment, the octane number of the hydrodesulfurization product is at least 90% and preferably at least 95% and more preferably at least 99% of the octane number of the feed.

[0025] The invention will be further described with respect to the following examples; however, the scope of the invention is not limited thereby. Unless otherwise specified, all parts and percentages are by weight.

EXAMPLES

[0026] 1. Synthetic Gasoline Feed

[0027] A synthetic gasoline feed was used for a catalyst activity test. It contained two olefins, octene-1,2,4,4-trimethylpentene-1, toluene, thiophene, pyridine, and n-heptane. The olefins were chosen to represent olefin distribution of typical cracking naphtha gasolines, that is 10-20% terminal olefins and 80-90% of branched olefins. Toluene was chosen to represent aromatics in gasoline factions. Thiophene was used to represent organic sulfur components in cracked naphtha gasoline. Pyridine was added to mimic basic components presented in cracked naphtha gasoline.

[0028] The amount of total olefins was varied in the range of 10-40%. The amount of aromatics was fixed to 40%. The amount of sulfur in the feed was varied in the range of 500-2500 ppm wt. The amount of pyridine was varied in the range of 50-250 ppm wt.

[0029] 2. Reactor Set-up

[0030] Catalyst in the form of pellets or small particles mixed with a diluent, e.g., silicon carbide, was loaded into the reactor. The reactor was made of stainless steel (OD: ½″, wall thickness of {fraction (1/16)}″, length: 8″). Typical diluent to catalyst ratio was 5-15 wt/wt.

[0031] The catalyst was positioned in between two quartz wool plugs to prevent catalyst from being carried away.

[0032] The reactants (hydrocarbon feed and hydrogen) were fed from the bottom. The liquid feed was delivered by an Eldex metering pump. Hydrogen was controlled by a Brooks mass flow controller.

[0033] Reactor pressure was controlled by a Mighty-Mite backpressure regulator.

[0034] Reaction products were analyzed by an on-line GC.

[0035] 3. Catalyst Activation

[0036] The catalyst was normally pre-sulfided with a sulfidation feed containing 2.7% dimethyldisulfide in n-heptane co-fed with hydrogen. Typical sulfiding conditions are: 0.1-0.3 g/min feed, 10-30 cc/min of hydrogen flow, final sulfiding temperature of 250-350° C. for 4-12 hours; total pressure: 100-400 psig.

[0037] 4. Hydrodesulfurization (HDS) Run

[0038] HDS feed was introduced once the reactor temperature was lowered to below 150° C. The reactor temperature was raised to the desired temperature for HDS. Typical HDS conditions were: 1-3 g catalyst, feed rate: 0.1-2 g/min; hydrogen flow: 10-200 cc/min; total pressure: 100-900 psig.

[0039] The selectivity of the hydrodesulfurization of the present invention may be expressed as a Selectivity Factor, as follows:

Selectivity Factor=A*(A/B)

[0040] wherein A is the rate of hydrodesulfurization and B is the rate of hydrogenation of olefins, as a first order rate expressed per mole of metal in the catalyst.

[0041] The following examples compare the Selectivity Factor for conventional catalysts with the Selectivity Factor achieved in accordance with the invention (Table 3).

[0042] 5. Catalysts

[0043] 5.1 Commercial CoMo/Al₂O₃

[0044] A commercial CoMo/Al₂O₃ catalyst (DC130) from Criterion was used for HDS activity test. This catalyst contains 4.3 wt % CoO and 20.5 wt % MoO₃.

[0045] 5.2 Commercial NiMo/Al₂O₃

[0046] A commercial NiMo/Al₂O₃ catalyst from Sud Chemie was also tested for HDS. This catalyst contains 3.5 wt. % NiO and 13.5 wt % MoO₃.

[0047] 5.3 PdPt/Ce-ZSM-5

[0048] The catalyst was prepared by incipient wetness impregnation of a Ce-ZSM-5 zeolite. For bimetallic, Pt was introduced first followed with Pd. An amount of 20 g of Ce-ZSM-5 (Ce: 5.3 wt %, SiO₂/Al₂O₃=53, from Zeolyst International) was impregnated with a solution containing 0.1195 g of platinumtetraamine nitrate (Alfa Aesar, 99.9% metal purity) to give 0.3 wt % Pt. The mixture was dried at 110° C. for two hours before calcined at 500° C. in air for 3 hours. Pd was introduced by incipient wetness impregnation of the 0.3 Pt %/Ce-ZSM-5 with a solution containing 0.5369 g of palladiumtetraamine nitrate (Alfa Aesar, 99.9% metal purity) to give 0.9 wt % Pd. It then followed the same procedure for drying and calcination to give the PtPd/Ce-ZSM-5 that contained 0.3% Pt-0.9% Pd.

[0049] 5.4 PdPt/H-ZSM-5

[0050] The catalyst was prepared by incipient wetness impregnation of an H-ZSM-5 zeolite. For bimetallic, Pt was introduced first followed with Pd. An amount of 20 g of H-ZSM-5 (SiO₂/Al₂O₃=53, from Zeolyst International) was impregnated with a solution containing 0.1195 g of platinumtetraamine nitrate (Alfa Aesar, 99.9% metal purity) to give 0.3 wt % Pt. The mixture was dried at 110° C. for two hours before calcined at 500° C. in air for 3 hours. Pd was introduced by incipient wetness impregnation of the 0.3Pt %/H-ZSM-5 with a solution containing 0.5369 g of palladiumtetraamine nitrate (Alfa Aesar, 99.9% metal purity) to give 0.9 wt % Pd. It then followed the same procedure for drying and calcination to give the PtPd/H-ZSM-5 that contained 0.3% Pt-0.9% Pd.

[0051] 5.5 Pd/TF-Al₂O₃

[0052] This catalyst was prepared by incipient wetness impregnation of a thin film alumina. The thin film alumina contains 20 wt % of γ-alumina on α-alumina. This thin film support was prepared by fluid bed coating of 1-2 mm α-alumina micro-spheres (Norton Chemicals) with an alumina sol (Nyacol Chemicals). An amount of 20 grams of the thin film catalyst support was incipient wetness impregnated with a solution containing 0.2311 g of palladium tetraamine nitrate (Alfa Aesar, 99.9% metal purity) to give 2.0 wt % Pd on the basis of the thin film γ-alumina. The mixture was dried at 110° C. for two hours before being calcined at 500° C. in air for 3 hours. This catalyst was designated as 2.0% Pd/TF-Al₂O₃.

[0053] 5.6 1 % Ru/(CeO₂+Al₂O₃)

[0054] This catalyst was prepared by incipient wetness impregnation of a mixed oxide of ceria and alumina. The mixed oxide containing 70% ceria and 30% alumina was prepared by co-gelation of a ceria sol and alumina sol (both from Nyacol Chemicals) followed with drying and calcination at 700° C. for 4-10 hours. Amount of 20 grams of the mixed oxide was incipient wetness impregnated with a solution containing 0.5799 g of ruthenium tetraamine nitrate (Alfa Aesar, 99.9% metal purity) to give 1 wt % Ru on the mixed oxide. The mixture was dried at 110° C. for two hours before calcined at 500° C. in air for 3 hours.

[0055] Table 3 summarizes the HDS results obtained on a number of commercial and own catalyst formulations at 215° C., 440 psig, hydrocarbon feed rate of 0.1-2 g/min/g-catalyst, and hydrogen flow of 5-100 cc/min/g-catalyst. The results presented in Table 3 are steady-state performance, typically after a time on stream of 6-20 hours, depending on catalyst and feed rate. TABLE 3 Summary of Overall HDS Performance of Commercial Catalysts and Catalysts of Present Invention Overall HDS Performance (normalized) Examples Catalyst Liquid Phase Gas Phase 1 CoMo/Al₂O₃ 1.0 1.0 2 NiMo/Al₂O₃ 0.9 1.5 3 PdPt/Ce-ZSM-5 14.6 42.4 4 PdPt/HZSM-5 22.0 11.1 5 Ru/(CeO₂ + Al₂O₃) 0.2 0.3 6 Pd/TF-Al₂O₃ 4.5 7.5

[0056] Examples 1 and 2 did not include an acidic support and also did not include a noble metal and did not provide an overall performance comparable to Examples 3 and 4, which are in accordance with the invention

[0057] Table 4 presents acidity information of the catalyst supports. The acidity was measured using a temperature programmed desorption technique, where isopropylamine was adsorbed first at 100° C., then purged in nitrogen flow until no further weight change. A temperature ramping was carried in nitrogen at 10° C./min from 100° C. to 600° C. The weight loss as a function of temperature was a measurement of amount of isopropylamine adsorbed by the catalyst and peak position was a measurement of interaction between the acid sites and IPA. Higher desorption temperature indicates stronger acid sites. TABLE 4 Summary of Acidity Measurement Results of Catalysts and Catalyst Supports of Present Invention using IPA-TPD TPD Characteristics Strong Weak Acid Sites Acid Sites Example Catalyst (mmol/g) (^(a)) (mmol/g) (^(b)) SWAR (^(c)) 10 HZSM-5 0.58 0.74 0.79 11 2.36% Ce-HZSM-5 0.55 0.63 0.88 12 4.72% Ce-HZSM-5 0.54 0.58 0.94 13 9.44% Ce-HZSM-5 0.47 0.47 0.99 14 1% Pd-HZSM-5 0.66 0.33 2.00 15 1% Pt-HZSM-5 0.62 0.49 1.26 16 20% TF-Al₂O₃ 0.27 0.25 1.07 17 (CeO₂ + Al₂O₃) 0.30 0.20 1.50 18 Silica-Alumina 0.16 0.24 0.66

[0058] The number of acid sites and distribution of acid sites, i.e., strong versus weak can be modified by varying the supports. Through metal support interaction, optimal performance of catalyst for gasoline HDS can be achieved by tailoring the support acidity, i.e., number of acid sites and acid strength.

[0059] Numerous modifications and variations of the present invention are possible in light of the above teachings and, therefore, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. 

What is claimed is:
 1. A process for the hydrodesulfurization of an olefinic gasoline fraction, comprising: hydrodesulfurizing an olefinic gasoline fraction in the presence of a catalyst comprising a noble metal supported on an acidic support.
 2. The process of claim 1 wherein the gasoline fraction contains at least 100 ppm of sulfur.
 3. The process of claim 1 wherein the gasoline fraction contains at least 5% wt olefins.
 4. The process of claim 1 wherein the catalyst further includes at least one of Mo, W, Cr, or Re, Mn, Tc.
 5. The process of claim 1 wherein the acidic support is at least one of silica-alumina, alumina or a zeolite.
 6. The process of claim 1 wherein the acidic support has pores with a pore diameter from 0.4 nm to 150 nm and a surface area of from 1 m²/g to 1500 m²/g.
 7. The process of claim 1 wherein the catalyst has a size of from 0.2 micron to 10 mm.
 8. The process of claim 1 wherein the catalyst is installed within a catalytic distillation column.
 9. The process of claim 1 wherein the catalyst is installed in a fixed bed reactor.
 10. The process of claim 1 wherein the hydrodesulfurization is in the gas phase. 